I'm in the process of replacing rear shockers on my boggo A500 and I found the most accurate info (and some of the best prices) on buycarparts.co.uk  You can select your vehicle type or just put in your reg and various alternative replacement parts will be shown, often with details of OEM part numbers (but good luck with trying to read those off a shock absorber...).  I'm keeping mine stock - the ride is bad enough as it is! Trying to eliminate some of the skipping by having Powerflex bushes fitted to the rear suspension beam. The Pf bushes I bought for the top eye of the new shockers won't fit  - they seem to be designed solely for standard Fiat 500s, with a larger diameter eye. Hey ho.